TAMPER-EVIDENT LID FOR PLASTIC CONTAINERS

Abstract: A tamper-evident seal for plastic containers of the type which includes a tray and a lid (2) with a flat wall (4). The tray and the lid have respective complementarily shaped edges (7; 11) with outer peripheral portions (8; 12) that are substantially vertical or slightly inclined. Protrusions (14) are arranged along the outer peripheral portion (12) of one of the edges and are suitable to elastically and unidirectionally couple by pressing within slots (15) which are arranged along the outer peripheral portion (8) of the other edge. The protrusions (14) are substantially radial with respect to the outer peripheral portion (12) of the edge on which they are formed and are shaped like teeth which are slightly inclined outward. The openings (15) are substantially parallel to the outer peripheral portion (8).

Description: TAMPER-EVIDENT LID FOR PLASTIC CONTAINERS The present invention relates to a tamper-evident seal for plastic containers of the type that includes a tray with side and bottom surfaces and a lid with a substantially flat wall , wherein the tray and the lid have respective complementarily shaped edges with a peripheral external po rt ion that i s subs tant i a l ly vert i ca l o r s l i gh t ly inclined with respect to the vertical . Tamper-evident seals of the type described above are known which are particularly suitable for containers that have a generally rectangular or polygonal plan shape. These known seals include one or more pairs of engagement parts, for example shaped like pins with arrow-shaped tips that engage in complementarily shaped elastic cavities, arranged along the edges of the tray and of the container respectively at the corners of the container. These engagement parts are adapted to cooperate unidirectionally when closing the container, so that in order to release the lid it is necessary to break them, i.e. separate them from the corresponding portion of the tray or lid by levering between them or by acting on adapted grip wings. The possible shapes of the containers are limited by the arrangement of these conventional seals at the corners. While containers that have for example a circular shape must be provided with a series of radial wings on which the seals are formed, with evident higher manufacturing costs and greater bulk of the finished product. Furthermore, in this type of seal the engagement action is applied locally and is not uniformly distributed along the entire extension of the edge. Another drawback of conventional tamper-evident seals is the fact that in order to obtain strong engagement parts and because of their relative complexity, the lid and the tray must be produced by injection-molding, and it is not conceivable to use a process for molding thermoplastic material. Furthermore, in some known types of seal one of the engagement parts, after opening, can remain loosely attached to the corresponding edge, and may accidentally fall inside the container. Also, in many cases it is not possible to positively check whether the seal has been broken, and consequently the user is not truly assured of the integrity of the package. The aim of the present invention is to el iminate the drawbacks described above by providing a tamper-evident seal that can be applied on containers of any shape without altering the outer profile of the tray or of the lid. An object is to provide a tamper-evident seal that can be produced indifferently with a process for the molding of thermoplastic sheets or for the inj ection-mo lding of melted plastic material , so as to achieve savings in production. Another object is to provide a tamper-evident seal that extends along the entire circumference of the lid and must be removed completely to allow to open the container. This aim, these objects and others which will become apparent hereinafter are achieved by a tamper-evident seal for plastic containers of the type which includes a tray with side and bottom surfaces, and a lid with a substantially flat wall, the tray and the lid having respective complementarily shaped edges with an outer peripheral portion that is substantially vertical or slightly inclined, characterized in that it comprises a first engagement means which is distributed along the outer peripheral portion of one of the edges and is suitable to elastically and unidirectionally couple by pressing within a second complementarily shaped engagement means which is distributed along the outer peripheral portion of the other one of the edges. With an arrangement of this kind, the seal can be applied to containers having any shape, for example a circular one, since it is not necessary to have a corner or a protrusion of the edges in order to place the engagement parts . Furthermore, the engagement means is distributed along the entire circumference of the closing edges, with greater assurance of a hermetic seal. Finally, any tampering with the seal is clearly evident on the outside by virtue of the peripheral position of the engagement means . Advantageously, the first engagement means can be constituted by a series of protrusions which are substantially radial with respect to the outer peripheral portion of the edge on which they are formed. Preferably, the protrusions consist of a plurality of teeth which are slightly inclined outward and are approximately shaped like a trapezium, with the longer parallel side directed inward, and are formed monolithically with the corresponding outer peripheral portion in angularly equidistant positions along its extension. The second engagement means can be constituted by a series of openings which are substantially parallel to the outer peripheral portion of the edge on which they are formed. Advantageously, the openings are formed by a strip of material which is joined to the corresponding edge by a series of transverse wings that are at least equal in height to the maximum thickness of the protrusions, in angularly equidistant positions that match those of the protrusions. Conveniently, the wings taper upward at the region where they are connected to the outer peripheral portion of the corresponding edge, and the connection region has a smaller tear-resistant cross-section than the region for connection to the strip. According to the invention, the strip can have a substantially radial grip tab with a transverse cross- section that is at least equal to the maximum cross- section of the wings, and has a transverse notch in a position which is adjacent to a lateral corner of the grip tab so as to form a region for the prefracture and initial breaking of the strip and for the subsequent separation of the wings from the peripheral portion of the edge to which it is connected. By virtue of this embodiment of the seal, both the tray and the lid can be obtained indifferently with an injection-molding process or with a process for the forming of plastic sheets, ensuring the same mechanical strength as conventional seals at distinctly lower costs. Further character i s t i cs and advantage s wi l l be come apparent from the following detai led description of an exemplifying but non-limitative embodiment of a seal according to the invention, illustrated with the aid of the accompanying drawings, wherein: Figure 1 is a front and partially sectional view of a tray and of a lid with a tamper-evident seal according to the invention, prior to closure; Figure 2 is a front enlarged-scale view of a detail of Figure 1, with the container closed; Figure 3 is a sectional view of the detail of Figure 2, taken along the plane III-III; Figure 4 is a sectional view of a detail of Figure 3, taken along the plane IV-IV. With reference to the above figures, a container for food or other commercial products is generally designated by the reference numeral 1. The container includes a lid 2 with a substantially flat central wall 4 and a tray 3 with a side wall 5 and a bottom wall 6. Both the lid and the tray can be made of plastic, such as polyethylene, polypropylene, PVC or other equivalent materials, using injection-molding processes or by forming sheets of preheated material. The lid 2 has a folded edge 7 with an external peripheral portion 8 which is approximately vertical or, better still, is slightly inclined by approximately 10° to facilitate extraction, and is joined to an internal peripheral portion 9 by an annular region 10 which is approximately flat and horizontal. The tray 3 has a folded edge 11 with an outer peripheral portion 12 which is also inclined by approximately 10° and is joined to the side wall 5 by means of an annular region 13 which is approximately flat and slightly inclined with respect to the horizontal. The edges 7 and 11 are substantially complementarily shaped in order to sealingly couple mainly along their respective internal and external peripheral regions even after the first opening action. Conveniently, according to the invention, a respective engagement means is distributed along the outer peripheral portions 8 and 12 of the edges 7 and 11 and is suitable to be elastically and unidirectionally coupled by pressing in order to hermetically close and seal the container. In particular, along the outer peripheral portion 12 of the tray there is a series of protrusions or teeth 14 that extend radially and are inclined outward at approximately 40° with respect to the peripheral portion 12. The protrusions can be shaped approximately like a trapezium in which the longer parallel side is joined to the peripheral portion 12, with a maximum height S and a width L. Along the peripheral portion 8 of the edge of the tray there is a series of openings or slots 15 in angularly equidistant positions which match those of the protrusions 14. Conveniently, the openings 15 are formed by a strip 16 that runs uninterruptedly along the circumference and is joined to the peripheral portion 8 by transverse wings 17. The wings 17 have an approximately pyramid-like shape which tapers upward and have upper and lower connecting regions 18 and 19. The resisting cross-section of the connecting regions 18 is relatively smaller than that of the regions 19. The minimum width W of the openings 15 between the bases of the wings 17 is greater than the width L of the protrusions 14. After filling the tray, the packager moves the lid closer and compresses it toward the tray so as to align the protrusions 14 with the openings 15, causing the engagement of the protrusions in the openings. The lid cannot lift due to the negative-allowance fit of the upper edge 16' of the strip 16 against the base of the teeth 14. Conveniently, a tab 20 for grip on the part of a user is joined to the strip 16. As shown more clearly in Figure 4, the strip has, at one of the corners of the tab 20, a wedge-shaped notch or prefracture 21 that forms a stress raiser of the strip. A consumer can see that the container is sealed by the presence of the strip 16. When the consumer wishes to open the container, he/she can grip the tab 20 and pull it outward and upward, breaking the strip at the notch 21. As the pulling action continues, the consumer separates the strip from the outer peripheral portion 8 at the connecting regions 8 that have the smallest resisting cross-section. In this manner the lid is released and can be lifted. In subsequent use, as already mentioned, tightness is in any case ensured by the contact of the facing surfaces of the inner and outer peripheral portions of the complementary edges. The seal according to the invention achieves the intended aim and all the objects, and in particular it is noted that it can be applied to containers having any shape, even without corners. Furthermore, it can be obtained by means of processes for the forming of thermoplastic sheets or indifferently by injection. The seal according to the invention is susceptible to numerous modifications and variations, all of which are within the scope of the inventive concept expressed in the accompanying claims and are considered to be equally protected. Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly, such reference signs do not have any limiting effect on the scope of each element identified by way of example by such reference signs.

Claims: CLAIMS 1. Tamper-evident seal for plastic containers of the type which comprises a tray (3) with side (5) and bottom (6) surfaces, and a lid (2) with a substantially flat wall (4), said tray and said lid having respective complementarily shaped edges (7; 11) with an outer peripheral portion (8; 12) that is substantially vertical or slightly inclined, characterized in that it comprises a first engagement means (14) which is distributed along the outer peripheral portion (12) of one of said edges and is suitable to elastically and unidirectionally couple by pressing within a second complementarily shaped engagement means (15) which is distributed along the outer peripheral portion (8) of the other one of said edges. 2. Seal according to claim 1, characterized in that said first engagement means comprises a series of protrusions (14) which are substantially radial with respect to the outer peripheral portion (12) of the edge on which they are formed. 3. Seal according to claim 2, characterized in that said protrusions (14) consist of a plurality of teeth that are slightly inclined outward and are shaped approximately like a trapezium in which the maximum height (S) is arranged inward and the maximum width (L) is preset. 4. Seal according to claim 2, characterized in that said protrusions (14) are formed monolithically with said outer peripheral portion (12) in angularly equidistant positions along its extension. 5. Seal according to claim 2, characterized in that said second engagement means comprises a series of openings (15) which are substantially parallel to the outer peripheral portion (8) of the edge on which they are formed and have a width (W) which is equal to, or greater than, the maximum width (L) of said protrusions (14). 6. Seal according to claim 5, characterized in that said openings (15) are formed by a strip (16) of material which is joined to the corresponding edge by a series of transverse wings (17) the height (H) of which is at least equal to the maximum height (S) of said protrusions (14). 7. Seal according to claim 5, characterized in that said openings (15) are formed in angularly equidistant positions that match those of said protrusions (14). 8. Seal according to claim 6, characterized in that said wings (17) taper upward at the region (19) for connection to the outer peripheral portion (8) of the corresponding edge. 9. Seal according to claim 8, characterized in that the region (19) for connecting said wings to the outer peripheral portion (8) of the corresponding edge has a smaller tear-resistant cross-section than the region (19) for connection to said strip (16). 10. Seal according to claim 6, characterized in that said strip (16) has a grip tab (20) which is substantially radial and has a transverse cross-section that is at least equal to the maximum cross-section of said wings. 11. Seal according to claim 10, characterized in that said strip (16) has a transverse notch (21) in a position which is adjacent to a lateral corner of said grip tab (20) so as to form a region for the prefracture and initial breaking of the strip and for the subsequent separation of the wings from the peripheral portion of the edge to which it is connected. 12. Seal according to one or more of the preceding claims, characterized in that said protrusions (14) and said openings (15) are formed monolithically with the edges of said lid (2) and of said tray (3) by injection-molding or by forming plastic sheets. 13. Seal according to one or more of the preceding claims, characterized in that said protrusions (14) and said openings (15) are formed respectively along the edge of the lid (2) and of the tray (3). 14. Seal according to one or more of the preceding claims, characterized in that said protrusions (14) and said openings (15) are formed respectively along the edge of the tray (3) and of the lid (2).

Inventors: CASARTELLI VANDA, CASARTELLI, VANDA
Applicants: CASARTELLI VANDA, RIGLIETTI ANTONIO, CASARTELLI, VANDA, RIGLIETTI, ANTONIO
Application year: 1994
Main classification: B65D43
IPC codes: B65D43